A. Brooks Harris

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Arthur Brooks Harris, called Brooks Harris, (born 25 March 1935) [1] is an American physicist.

Contents

Biography

Harris was born in Boston, Massachusetts, and studied at Harvard University with bachelor's degree in 1956, master's degree in 1959, and PhD in experimental solid state physics from Horst Meyer in 1962. [2] [3] Harris was in 1961/62 at Duke University to complete his doctoral thesis with Meyer and then was an instructor there from 1962 to 1964. During 1961–1964 at Duke University Harris retrained himself as a theorist in condensed matter physics and then spent the academic year 1964/65 as a researcher working with John Hubbard in the UK at the Atomic Energy Research Establishment (Harwell Laboratory) near Harwell, Oxfordshire. [2] At the University of Pennsylvania, Harris became in 1965 an assistant professor and in 1977 a full professor, continuing there until his retirement as professor emeritus.

He was a visiting professor at University of British Columbia in 1976, at the University of Oxford in 1973, 1986, and 1994, at Tel Aviv University in 1987 and 1995, and at McMaster University in 2005. He was visiting scientist at Sandia National Laboratories in 1974 and at the National Institute of Standards and Technology (NIST) in 2002. [2]

In 2007 he received the Lars Onsager Prize for his contributions to the statistical physics of disordered systems, especially for the development of the Harris criterion. From 1967 to 1969 he was Sloan Fellow and in 1972/73 a Guggenheim Fellow. In 1989 he was elected a Fellow of the American Physical Society.

Harris has been married to Peggy since 1958 and has three children, eight grandchildren, and two great-grandchildren.

Research

Upon receiving the Lars Onsager Prize, Harris wrote in 2007:

My interests have included orientational ordering in solid molecular hydrogen (some with H. Meyer), critical properties of numerous random systems (often in collaboration with T. C. Lubensky), the crystal structure and dynamics of fullerenes (often with T. Yildirim), spin dynamics of frustrated magnets (with A. J. Berlinsky and more recently with A. Aharony, O. Entin-Wohlman, and T. Yildirim) and the symmetry properties of frustrated magnets which exhibit simultaneous magnetic and ferroelectric ordering. [2]

He has also collaborated in theoretical condensed matter physics with R. J. Birgeneau (MIT), J. Yeomans (Oxford), R. D. Kamien (Penn), C. Broholm (Johns Hopkins), and A. Ramirez (Bell Labs). [4]

In 1973 he developed at Oxford the Harris criterion, [5] [6] which indicates the extent to which the critical exponents of a phase transition are modified by a small amount of randomness (e.g., defects, dislocations, or impurities). Such impurities "smear" the phase transition and lead to local variations in the transition temperature. Let denote the spatial dimension of the system and let denote the critical exponent of correlation length. The Harris criterion states that if

the impurities do not affect the critical behavior (so that the critical behavior is then stable against the random interference). For example, in the classical three-dimensional Heisenberg model and thus the Harris criterion is satisfied, while the three-dimensional Ising model has and thus does not satisfy the criterion (). [7]

Selected publications

Related Research Articles

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In chemistry, thermodynamics, and other related fields, a phase transition is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of matter: solid, liquid, and gas, and in rare cases, plasma. A phase of a thermodynamic system and the states of matter have uniform physical properties. During a phase transition of a given medium, certain properties of the medium change as a result of the change of external conditions, such as temperature or pressure. This can be a discontinuous change; for example, a liquid may become gas upon heating to its boiling point, resulting in an abrupt change in volume. The identification of the external conditions at which a transformation occurs defines the phase transition point.

The Ising model, named after the physicists Ernst Ising and Wilhelm Lenz, is a mathematical model of ferromagnetism in statistical mechanics. The model consists of discrete variables that represent magnetic dipole moments of atomic "spins" that can be in one of two states. The spins are arranged in a graph, usually a lattice, allowing each spin to interact with its neighbors. Neighboring spins that agree have a lower energy than those that disagree; the system tends to the lowest energy but heat disturbs this tendency, thus creating the possibility of different structural phases. The model allows the identification of phase transitions as a simplified model of reality. The two-dimensional square-lattice Ising model is one of the simplest statistical models to show a phase transition.

A conformal field theory (CFT) is a quantum field theory that is invariant under conformal transformations. In two dimensions, there is an infinite-dimensional algebra of local conformal transformations, and conformal field theories can sometimes be exactly solved or classified.

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Critical exponents describe the behavior of physical quantities near continuous phase transitions. It is believed, though not proven, that they are universal, i.e. they do not depend on the details of the physical system, but only on some of its general features. For instance, for ferromagnetic systems, the critical exponents depend only on:

In theoretical physics, massive gravity is a theory of gravity that modifies general relativity by endowing the graviton with a nonzero mass. In the classical theory, this means that gravitational waves obey a massive wave equation and hence travel at speeds below the speed of light.

The Kramers–Wannier duality is a symmetry in statistical physics. It relates the free energy of a two-dimensional square-lattice Ising model at a low temperature to that of another Ising model at a high temperature. It was discovered by Hendrik Kramers and Gregory Wannier in 1941. With the aid of this duality Kramers and Wannier found the exact location of the critical point for the Ising model on the square lattice.

In statistical mechanics, the two-dimensional square lattice Ising model is a simple lattice model of interacting magnetic spins. The model is notable for having nontrivial interactions, yet having an analytical solution. The model was solved by Lars Onsager for the special case that the external magnetic field H = 0. An analytical solution for the general case for has yet to be found.

<span class="mw-page-title-main">Percolation threshold</span> Threshold of percolation theory models

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<span class="mw-page-title-main">Quantum stirring, ratchets, and pumping</span>

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A composite fermion is the topological bound state of an electron and an even number of quantized vortices, sometimes visually pictured as the bound state of an electron and, attached, an even number of magnetic flux quanta. Composite fermions were originally envisioned in the context of the fractional quantum Hall effect, but subsequently took on a life of their own, exhibiting many other consequences and phenomena.

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In the context of the physical and mathematical theory of percolation, a percolation transition is characterized by a set of universal critical exponents, which describe the fractal properties of the percolating medium at large scales and sufficiently close to the transition. The exponents are universal in the sense that they only depend on the type of percolation model and on the space dimension. They are expected to not depend on microscopic details such as the lattice structure, or whether site or bond percolation is considered. This article deals with the critical exponents of random percolation.

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<span class="mw-page-title-main">Amnon Aharony</span> Physicist at Ben Gurion University in Israel

Amnon Aharony is an Israeli Professor (Emeritus) of Physics in the School of Physics and Astronomy at Tel Aviv University, Israel and in the Physics Department of Ben Gurion University of the Negev, Israel. After years of research on statistical physics, his current research focuses on condensed matter theory, especially in mesoscopic physics and spintronics. He is a member of the Israel Academy of Sciences and Humanities, a Foreign Honorary Member of the American Academy of Arts and Sciences and of several other academies. He also received several prizes, including the Rothschild Prize in Physical Sciences, and the Gunnar Randers Research Prize, awarded every other year by the King of Norway.

Shang-keng Ma was a Chinese theoretical physicist, known for his work on the theory of critical phenomena and random systems. He is known as the co-author with Bertrand Halperin and Pierre Hohenberg of a 1972 paper that "generalized the renormalization group theory to dynamical critical phenomena." Ma is also known as the co-author with Yoseph Imry of a 1975 paper and with Amnon Aharony and Imry of a 1976 paper that established the foundation of the random field Ising model (RFIM)

Fractional Chern insulators (FCIs) are lattice generalizations of the fractional quantum Hall effect that have been studied theoretically since early 2010. They were first predicted to exist in topological flat bands carrying Chern numbers. They can appear in topologically non-trivial band structures even in the absence of the large magnetic fields needed for the fractional quantum Hall effect. They promise physical realizations at lower magnetic fields, higher temperatures, and with shorter characteristic length scales compared to their continuum counterparts. FCIs were initially studied by adding electron-electron interactions to a fractionally filled Chern insulator, in one-body models where the Chern band is quasi-flat, at zero magnetic field. The FCIs exhibit a fractional quantized Hall conductance.

References

  1. biographical information from American Men and Women of Science, Thomson Gale 2004
  2. 1 2 3 4 "2007 Lars Onsager Prize Recipient: A. Brooks Harris, University of Pennsylvania". American Physical Society.
  3. A. Brooks Harris at the Mathematics Genealogy Project
  4. "A. Brooks Harris". Physics & Astronomy, University of Pennsylvania.
  5. A. B. Harris (1974). "Effect of Random Defects on the Critical Behavior of Ising Models". Journal of Physics C: Solid State Physics. 7 (9): 1671–1692. Bibcode:1974JPhC....7.1671H. doi:10.1088/0022-3719/7/9/009.
  6. A. Brooks Harris (2007). "A Brief History of the Harris Criterion". Bulletin of the American Physical Society. 52 (1). American Physical Society: D3.003. Bibcode:2007APS..MAR.D3003H.
  7. Thomas Vojta, Rastko Sknepnek (July 2004). "Critical points and quenched disorder: From Harris criterion to rare regions and smearing". Physica Status Solidi B. 241 (9): 2118–2127. arXiv: cond-mat/0405070 . Bibcode:2004PSSBR.241.2118V. doi:10.1002/pssb.200404798. S2CID   16979505.